This invention relates to solid state relays and, more particularly, to circuits for protecting solid state relays from damage caused by an output circuit current overload.
Over the years, a wide variety of solid state relays have been developed which use a power semiconductor as the output circuit switching device. Recently, some solid state relay circuits have been designed which employ metal oxide power semiconductor field-effect transistors (MOSFET's) as the output circuit switching device. Circuits of this type are disclosed in U.S. patent application Ser. No. 590,184, filed Mar. 16, 1984 and assigned to the assignee of the present application.
A major disadvantage to the use of many solid state relays is their lack of tolerance of current overloads in the output circuit. For example, even a brief short circuit across the load will usually result in catastrophic failure of the relay output circuit switching device.
Accordingly, it is an object of the present invention to provide a solid state relay which is not damaged by an output circuit current overload.
It is another object of the present invention to provide a circuit which automatically interrupts the flow of output circuit current in the event of an overload.